This invention relates to a yarn tension control apparatus and method. While the apparatus is adaptable to numerous uses and applications, the one discussed in this application for purposes of illustration is a yarn tension control apparatus which is used downstream of a yarn creel and upstream of a air jet entanglement texturizing machine. This type of machine is used to produce a soft, lustrous, fluffy yarn form "flat" multifilament continuous filament synthetic yarn. Tension control is crucial when supplying yarn to such machines, since excessive tension greatly reduces the effectiveness of the air on the fibers in causing them to entangle and loop in the proper manner. The result is a yarn which is second quality and which in subsequent manufacturing processes manifests itself in flat and shiny spots or bands in woven or knitted goods, and in dye shade variations.
As usually supplied to the texturizing machine, flat yarn is subject to substantial yarn tension variation. These differences may be due to differences in package size, with small packages generating higher tension; yarn path differences; yarn guide alignment and wear, and the distance the yarn must travel. Generally, the tension in the yarn as it is delivered to the texturizing machine should be minimal, since the texturizing process itself overfeeds the yarn to a predetermined extent to cause looping and entanglement of the yarns.
Tension on synthetic flat yarn beyond a minimal amount exhibits itself in elongation of the yarn. By estimating the elongation of the yarn from the creel and determining the elongation desired immediately upstream of the texturizing machine, a percentage of "excess elongation" can be determined. The goal is, then, to reduce the tension and hence the elongation of the yarn in a reasonably predictable manner to a desired degree.